To provide a heated toilet seat mounted with a flat heater on the surface of a toilet seat and excellently warmed soon, which has a uniform distribution of the temperature of a seat surface.

A flat heater for a heated toilet seat has a substrate sheet 10 disposed with power feed lines S1 and S2 connected to a power source, and a plurality of linear heat generators R parallelly connected to the power feed lines S1 and S2. The linear heat generator has a cross-sectional area set relatively larger at a part at which the linear heat generator R has an energization length set longer, and has a cross-sectional area set relatively smaller at a part at which the heat generator has an energization length set shorter. Accordingly, the linear heat generator R has a uniform heat per unit length during energization, and the temperature distribution of the seat surface is uniformized.